Carbon Disulfide & metabolites Chelating effects

on various essential trace metals

Carbon disulfide reacts with the amino groups of amino acids and proteins to form thiocarbamate in blood and tissues (1) thiocarbamates, possessing sulfhydryl groups, may chelate polyvalent inorganic ions. CS2 reacts with endogenous amines to form dithiocarbamates.(2) which could be metabolised back to CS2. An implication is the formation of acid labile CS2 (AL CS2) will continue to increase, even at steady-state concentrations of CS2,as long as free CS2 is available to the tissue and adequate amine substrates are available. (2) An additional important finding was the slow elimination of AL CS2, suggesting that AL CS2may accumulate in the body after repeated exposure to CS2. (2) Dithiocarbamates are capable of chelating several polyvalent inorganic ions such as copper and zinc, and thus may inactivate numerous enzymes in which these ions are essential for activity. (3)

The hypothesis of a chelating effect has been supported by the results of some studies (4), Andreva who reported an increase in zinc and copper excretion in exposed rats, and Lukas et al. (5), who found increased copper levels in the peripheral nervous tissue of exposed rats.

Copper and zinc ions are essential for the prosthetic groups of many enzymes. The neurotoxic action of carbon disulfide and its interference with the activity of many enzymes could partly be explained by chelating effects. Zinc is required for the activity of enzymes such as lactic acid dehydrogenase a, carbonic anhydrase, glutamate dehydrogenase, and alcohol dehydrogenase. Copper, represents a cofactor of pyridoxol, a form of vitamin B6. Copper is required for the proper functioning of enzymes such as cytochrome c oxidase, the coenzyme A dehydrogenase system, and dopamine ß hydroxylase. The loss of copper from the spinal cord is accompanied by cellular damage, producing tissue degeneration. Disturbances of the central and peripheral nervous systems, resulting from carbon disulfide exposure, could be connected with the loss of copper due to chelation and consequent inhibitory effects on enzyme systems (6)

LOX, Lysyl oxidase is copperdependent. The LOX activity are essential for the mechanical stability of the fibers and other supramolecular assemblies formed by these proteins and the elasticity of elastin. Because collagens and elastin are important components of the extracellular matrix, abnormalities in their modification can be expected to affect many tissues, as seen in lathyrism, a connective tissue disorder caused by the administration of ß-aminopropionitrile, an irreversible inhibitor of lysyl oxidases. (7)

Extracellular copper enzymes initiate the formation of the lysine and hydroxylysine derived crosslinks in collagens and lysine-derived crosslinks in elastin. (8) CS2-mediated protein cross-linking occurs in vivo through the generation of Lys-Lys thiourea and that diethyldithiocarbamate can, through in vivo release of CS2, produce the same cross-linking structure. This observation supports the utility of cross-linking of peripheral proteins as a specific dosimeter of internal exposure for CS2 and provides a mechanistic explanation to account for the high-molecular-weight neurofilament protein species isolated from rats exposed to CS2 or N, N-diethyldithiocarbamate. (9)

Hight levels of homocysteine will irreversibly ihnibit LOX. (10) One study suggest that LDL downregulation of LOX could contribute to the endothelial dysfunction caused by hypercholesterolemia, thus contributing to atherosclerotic plaque formation. (11)

Enzyme inhibition

Tryptophan: Significant alterations of the metabolism in rats. Exposure to carbon disulfide can cause a significant increase in the activities of kynureninase and kynurenine-2-oxoglutarate aminotransferase in the kidneys, but only a slight increase in their activities in the liver. (13) changes in the tryptophan metabolism, manifested by increased excretion of xanthurenic acid in human (14)

Ca2+ UCP, peroxidation

The acute toxicity of organic toxicants like Carbon Disulfide has been linked to altered Ca2+ homeostasis through several mechanisms. (26 – 29)

Exposure of hepatocytes to halocarbons or carbon disulfide results in the rapid loss of Ca2′-ATPase activity and the ability of the endoplasmic reticulum to sequester Ca2 (30 -32)Maintenance of normal [Ca2+]i homeostasis is also dependent upon the status of other cell constituents, including sulfhydryl, glutathione, and nicotinamide-nucleotide redox levels of the cytoplasm and mitochondria. (33)

Chronic CS2 exposure resulted in inhibition of respiration and cytochrome oxidase activity in rat brain. Acute exposure showed partial uncoupling of the oxidative phosphorylation in rat brain. There was also a decrease of ATPase activity in rat brain. (34)

Oxidation stress also resulted in Ca(2+) concentrations and calmodulin (CaM) levels increases in cerebral cortex, hippocampus and spinal cord. Thus, CS(2) intoxication was associated with elevation of lipid peroxidation (LPO) and reduction of antioxidant status. It was suggested that ROS and concomitant LPO, at least in part, were involved in CS(2)-induced neuropathy. (35)

Cancer and p53

The p53 gene has been proposed as tumour suppressor and a candidate susceptibility gene in schizophrenia. (36) it is just a coincidence that the results of one study indicate that occupational exposure results in a significant increase in P53 CGT>CTT transversions. (37) identified occupational exposure in combination with smoking as a significant risk factor for the mutation. It was concluded that AS-PCR of the P53 273rd codon transversions is a suitable technique for studying the effects of occupational exposure to CS2.